"My first reaction is sympathy, I mean I feel pretty bad for the victims and their families. I don't like it at all. Beyond that, well, how would you feel if ... the bad guy watched what you do on TV and started calling [you] the 'ABC Killer?' That's pretty much how I'm reacting," Newmark said. "It just feels bad. You know, remember, I'm spending a great deal of time here fighting bad guys."

Markoff denies all the charges, but police say there's ample evidence linking him to the crime, including plastic restraints similar to those used in the murder, a gun found in his apartment that allegedly links him to the shooting and even the underwear of the victim. Markoff is now sitting alone in a Boston jail cell, on suicide watch.

Prostitution Promotion?

Craigslist is now one of the most-visited Web sites on the planet. Newmark's online service allows users to post advertisements for everything from yard sales to massage services. Every major city in America has its own Craigslist, and there are hubs overseas. Most of the postings are free, and there are separate sections for jobs, apartments and social events.

But there are also sections called "Casual Encounters" and "Erotic Services."

The site has been criticized by Massachusetts Attorney General Martha Coakley and Connecticut Attorney General Richard Blumenthal. "Craigslist is the largest source of prostitution in America," said Cook County Illinois Sheriff Tom Dart.

"Sometimes a bad guy of some sort tries to pull a fast one on our site. We don't want it there, it's wrong, and that's why we have the help of the general community and the law enforcement community getting rid of things like that," he said.

Prostitution aside, the site was linked with several violent crimes in recent years.

This month Michael Anderson was found guilty of shooting a woman to death lured to his apartment by a Craigslist ad. Earlier this year New York radio reporter George Weber was stabbed 50 times in his Brooklyn apartment, murdered by a man who answered Weber's ad on Craigslist offering $60 for "rough sex." In January Willie Donaldson was indicted for fatally shooting Michael Hicks, a man he met on Craigslist in Arlington, Virginia. Donaldson's attorney argued that his client fired at Hicks in self-defense.

Crime on Craigslist

Craigslist CEO Jim Buckmaster said the 50-million strong Craigslist community has a low incidence of crime.

"Now the risk is not zero, and no occurrence of violent crime is acceptable," Buckmaster said.

Newmark echoed Buckmaster's comment, saying, "I'm very proud that our site is composed of people who are overwhelmingly trustworthy and good. I am very proud that there is very little crime on our site, proportionately. Compare that to any other American community, look at the numbers."

As a private company, Craigslist is under no obligation to publish its financial records, and it has never done so. But industry experts estimate the site made between $60 and $80 million last year alone.

Last November Buckmaster said Craigslist will donate 100 percent of its net revenues from erotic services ads to charities.

"We always think that we should be doing more," said Buckmaster. "Anytime something like this happens, and even if it's not happening, we are looking for ways to improve the site. Not just in this area, but in all areas."

On Wednesday Blumenthal asked Craigslist to stop what he calls "pimping and prostitution in plain sight."

Blumenthal urged the site to take down pornographic photographs, hire more staff to enforce standards and fine users who violate the site's terms and conditions. Buckmaster and Newmark have not yet identified any specific actions Craigslist will take to prevent crime or police the site.

"We love to get constructive criticism, suggestions and ideas from law enforcement. We consider them partners," Buckmaster said. "Anything that Attorney General Blumenthal suggests we should have a hard look at in these areas, that's what we are going to do. We aren't comfortable with any crime happening on Craigslist, and we are going to keep working, as we announced with the attorney general, that we are going to keep working and adopting new measures until we get that off the site."

Tough Task of Policing Craigslist

Newmark said he regularly polices the site for illegal ads and responds to users, often working from 8 a.m. to 11 p.m.

"I just, as of today, accumulated all of the e-mails that I received over the year, so I was able to do a count, and it's 195,000 e-mails that I received over the last 365 days. And I know that I'm sending out roughly 40,000 e-mails per year," he said.

But with a staff of fewer than 30 people, and more than 40 million new classified ads posted every month, it's virtually impossible to keep track of every advertisement.

Craigslist does allow users to flag inappropriate items on the site, part of Newmark's effort to preserve Craigslist as a "free, open democratic system," albeit one that isn't perfect.

"If you see something that's wrong with our site, you can flag it for removal, and if other people agree with you, they can flag it also. And if enough people flag the ad, it will be removed automatically," he said. "The system works pretty well, not perfect. Some misconceptions about that are that often ads are removed and people think they are still there because the ad is still in their browser. That's something that I have to explain to someone about every day."

Currently, Newmark does not plan to shut down the erotic services section.

"Every section on Craigslist is based on community feedback. People in law enforcement and related areas told us that they want us to isolate some of the, some kinds of ads in their own particular categories," he explained. "For example, we have erotic services, because that concentrates legitimate erotic services in one area, so people know what they are going to see when they get there. This has been reinforced very strongly recently by the law enforcement."

In a 2006 interview with "Nightline", Newmark also defended the erotic services section, saying, "People would find other ways to do it," he said. "It would spread to other, more legitimate sections of our site."

On May 3 Newmark will attend a benefit concert in Minnesota for a scholarship fund at St. Olaf College in memory of 24-year-old Katherine Olson, who responded to a Craigslist ad for a nanny, and was murdered by the man who had placed the ad.

Newmark says he'll always be committed to the community he formed and now serves.